Method of converting magnesium dust into compact metallic magnesium



Dec. 12, 1939. E 'DM NN 2,183,392

METHOD OF CONVERTING MAGNESIUM DUST mo COMPACT METALLIC MAGNESIUM FiledAug. 2, 1938 Patented-Dec. 12, 1939 UNITED STATES Mri'rnon 0F CONVERTINGMAGNESIUM DUST INTO COMPACT METALLIC MAG- NEsrn Konrad Erdmann,Radcnthein, Germany, assignor to American Magnesium Metals CorporationPittsburgh, Pa.,

ware

a corporation of Dela- Application August 2, 193a, Serial'No. 222,624 InAustria August 16, 1937 5 Claims.

This invention relates to a process for the conversion of magnesium dustinto compact magnesium metal.

The object of the'present invention is'to provide a simple andeconomical method for recovering compact metal from magnesium dust byvaporization of the magnesium and re-condensation of the vapors.

A further object is to enable the, metal vapors to be disengagedpractically free from dusty impurities.

In the course of the electrothermic production of magnesium metal bysmelting magnesium oxide or prime materials containing magnesium oxide,

' with the aid of carbon, there is obtained'in the first stage ofoperation, on the condensing of the magnesium disengaged in the form ofvapor, as an intermediate product a dusty condensate containing 50 to 90percent of metallic magnesium while the remainder substantially consistsof magnesium oxide and carbon, all these constituents being contained inthe dusty condensate in a state of extremely fine division. Themagnesium is recovered from this dust, in a second stage of operation,by distillation or sublimation.

If in thissecond stage the magnesium dust were to be subjected, just asit is, to distillation or sublimation there would result, as the finalproduct, metal heavily contaminated with nonvolatile impurities, sinceowing to the very small volatile additions (such as carbon and magnesiumoxide), impasting the mixture with the aid of hydrocarbon oilnanddriving off the oil preferably 2 at a temperature at which a part of theoil will crack to'form a firmly coherent coke matrix;

Later it has been found thatit would befsimpler and-more economical-toform the pulverulent mixture for the pur'pose in question into compactedbodies by molding the same under high 1 pressure, preferably in anatmosphere of gas indifierent to magnesium, without the additioncfanybinding-material. However, the briquettes or the like produced in thismanner are of inadequate strength, so that particularly in the carryingout of the distillation or sublimation by passing the briquettes througha furnace'injan' undenser, which trouble increases rapidly with theprogressive driving off of the magnesium, since the remainder 'of thepieces, the skeleton so to speak, gets more and more light and porous.This difliculty becomes particularly troublesome in connection with theworking up of dust very rich in magnesium. Attempts undertaken with theview of enhancing the strength of the compacted bodies by considerablyincreasing the amount of nonqvolatile substances by means of additionsensuring the continued stability of the pieces during and after thefinal distillation operation have been made in vain; when transformingthe dust into compacted bodies by simply molding the same under highpressure without having recourse to the use of other expedients forincreasing the coherence no appreciable improvement could be achievedeitherby the admixing of finely divided-carbon such as soot, or by theadmixing of finely divided magnesium oxide to the material to bebriquetted.

According to the present invention, the departicularly to the addition.of binding material,

'finely ground residues left behind as the nonvolatile. remainder in thedistilling out or sublimingout of the" magnesium from such bodies in aprevious working operation. It-has surpris ingly transpired that,- as aresult of admixing such residues, the strength of the molded bodies issuddenly andgreatly improved, as may be seen from the followingcomparativetable:

Crushing strength in ices/0111.

Material briqu'ctted' Before After distildistillalation tion Dust(containing 32% of Mg) by itself. 113 0 Same dust 30% of dead burnedmagnesite... 62 0 Same dust -l- 30% of soot 0 Same dust 30% ofanthracite 50 0 Same dust 30%,0! bituminous coal coke... 15 0 Same dust30% of residues from preceding distillation runs 137 '39 For putting'theprocess into practice, the re sidue left behindas'the non-volatileremainder in a preceding working operation, e, g, distillationoperation, is ground and then sifted so as to obtain a. fine mealfraction containing of particles smaller than 0.0l mm., whereas thecoarser particlesare withdrawn; The line meal fraction is intimatelymixed with the magnesium dust to be worked up and the mixture thenmolded under a high pressure, for instance of the order of 1000kg./cm.=, to be formed into bodies of a diameter between 30 and 50 mm.The amount of the residue to be introduced depends on the magnesiumcontent of the dust. It has proved suitable to adjust this amount insuch a manner that the metal content in the compacted body does'notexceed The whole series of operations has to be carried out underexclusion of air, preferably in'an inert atmosphere, for instancehydrogen.

The vapor cooled may be. condensed either to av liquid deposit, whichsets to reguline metal, or directly from the vapor phase to a soliddeposit capable of coalescing under heat.

The drawing shows diagrammatically an apparatus adapted for carrying outthe process by way of example.

The spent residue leaving the plant I in which the preceding workingoperation has taken place passes through the condenser 2 into alock-chamber 3 delivering 70% of the amount collected into trucks to betaken to the waste dump. The remainder is carried by a suitable conveyor5a to a stock vessel 4, whence the material is delivered in properlyadjusted portions, by a conveyor 5b to the ball mill 6 provided with asifter. The material that fails to pass through the screen drops into asuitable receptacle, while the material passing through the screen istaken by a conveyor into the head of a mixing bunker 1 into which at thesame time the required amount of magnesium dust to be worked up isintroduced by a con-. duit I so as to bring together the same there withthe finely ground residue. The mixture is fed into a briquetting press 9of the known type used in briquetting lignite, whence the compactedbodies are passed. by a suitable conveying device, to the distillingfurnace. I claim:

1. Process of converting magnesium dust into compact metallic. magnesiumby extracting the magnesium content therefrom by means of vaporizationand subsequent re-condensation of the vapor, which process comprisesmixing themagnesium dust with ground residue leftbehind as thenon-volatile remainder in a previous operation involving vaporization ofmagnesium from magnesium dust, making the mixture into com; pactedbodies under high pressure without the addition of binding material;subjecting the briquettes thus obtained to afiheat treatment to driveout the magnesium in'the form of vapor;

and condensing the vapor evolved.

2. A process of converting magnesium dust into compact metallicmagnesium by extracting the magnesium content therefrom by means byvaporization and subsequent -re-condensation of the vapor, which processcomprises mixing themagnesium dust with ground residue left behind asthe non-volatile remainder in a preceding operation involvingvaporization of magnesium from magnesium dust, forming the mixture intocompacted bodies under high pressure without having recourse to otherexpedients for increasing the coherence, and then interposing thecompacted bodies thus obtained as resistor between the poles in anelectric furnace to drive out the magnesium in the form of vapor, andcondensing the vapor. 3. Process of converting magnesium dust intocompact metallic magnesium by extracting the magnesium content therefromby means of vaporization and subsequent re-condensation of the vapor,which process comprises mixing the magnesium dust with ground residueleft behind as the non-volatile remainder in the extracting of themagnesium in a previous operationinvolving vaporization of magnesiumfrom magnesium dust andmolding the mixture into strongly compactedbodies without the'addition of binding material, both these operationsbeing carried out under exclusion of air, and then subjecting thebriquettes thus obtained to a heat treatment to drive out the magnesiumin the form of vapor, and condensing thevapor evolved.

4. Process of converting magnesium dust into compact metallic magnesiumby extracting the magnesium content therefrom by means of vaporizationand subsequent re-condensation of the vapor, which process comprisesmixing the magnesium dust with finely ground spent residue left behindas the non-volatile remainder in a preceding operation involvingvaporization of magnesium from magnesium dust, briquetting the mixtureunder high pressure without the-addition of binding material, both theseoperations being carried out in an atmosphere of inert gas, and thenheating the briquettes thus obtained to vaporize the magnesium, andcondensing the vapor evolved to a liquid deposit which sets to regulinemetal.

-5. Process of converting magnesium dust into compact metallic magnesiumby extracting the magnesium content therefrom by means of vaporizationand subsequent re-condensation oi the vapor, which process comprisesmixing the magnesium dust with finely ground spent residue left behindas the non-volatile remainder in a preceding operation involvingvaporization of magnesium from magnesium dust, molding the mixture underhigh pressure into compacted bodies without the addition of bindingmaterial, heating the briquettes thus obtained to vaporize themagnesium, and condensing the vapor evolved directly from the vaporphase to a solid deposit capable of coalescing under heat.

7 KONRAD ERDMANN.

